The present invention relates to a fixed or self-propelled apparatus for distributing and producing cement mixes, substantially concrete, directly at the time of use in building yards and the like.
Conventional cement mixes, and particularly concrete for casting into formworks or the like, are usually constituted by proportioned mixes of inert materials, such as sand, gravel and others, with cement of various kinds and with water: the dosage of the components and of the water is chosen according to the structural characteristics which the concrete is to have and according to the type of use thereof.
Cement mixes are currently usually produced in fixed plants which are specifically equipped, and the resulting product is then transferred to building yards or the like by means of well-known truck mixers, i.e., trucks provided with an inclined and continuously rotatable container inside which the mixture of the components is kept under agitation to prevent changes in the characteristics and properties of the concrete during transport. It is also known that in order to allow the concrete to preserve its strength as much as possible during transport, the fixed mixing plant must be equipped with a forced premixing device.
Accordingly, truck mixers can be loaded only from a specific plant and after filling it is impossible to proportion the cement and the water.
The degree of preservation during transport by means of truck mixers is acceptable only for trips limited to a few kilometers and with the aid of suitable additives; moreover, the transport of the ready-mixed concrete in truck mixers also entails the drawback that considerable time and a very high consumption of energy and water are required for the loading, transport, unloading and washing operations.
In order to obviate the drawbacks entailed by the use of truck mixers to transport the ready-mixed concrete, mixing equipment or plants have already been proposed which are structured so as to simultaneously perform at the building yard the mixing of the materials that constitute the concrete and the subsequent unloading into the formworks; in this manner, the well-known deteriorations of ready-mixed concrete caused by transport are avoided and significant advantages are allowed in practice as regards precision in the dosage and mixing of the components, graduality of unloading, and therefore better uniformity and greater strength of the resulting product.
However, even this method has some drawbacks, especially as regards the energy consumption required by the mixing apparatus. This arises from the fact that the inert products and the cement are made to advance horizontally by means of a conveyor belt which receives the proportioned amounts from overlying containers and are then sent into a screw mixer, into which the mixing water is also sent; said mixer is arranged with a vertical or optionally inclined axis in order to allow the mixed product to rise and exit upwards and then enter the formworks by means of chutes. The vertical arrangement of the mixing screw therefore requires the use of high power to make the product rise along said screw up to the upper exit end; the screw mixer is also usually provided with an inclination which can vary both longitudinally and transversely with respect to the containers of the components, and this entails in practice a considerable bulk.